1. Field of the Invention
The invention relates generally to the field of chemistry. In particular the invention involves compositions and methods that may be used in water purification.
2. Description of Related Art
Arsenic is a naturally-occurring element in the surface and subsurface environment that ranks 20th in abundance in the earth's crust. Arsenic is present at very low concentrations in rocks and soils, which are the prime sources of arsenic in ground water. However, some arsenic in ground water is likely leached from sulfide minerals within bedrock and transported to aquifers. Sulfide minerals, in particular, are known to contain high concentrations of arsenic.
Arsenic in water occurs in two valance states, arsenite (As III) and arsenate (As V). Natural ground water contains As(III) since the reducing conditions prevail. On the other hand, As(V) is the dominant species in surface water. The exposure of humans to such arsenic contaminated water is a major concern world wide. For example, arsenic exposure has been associated with the development of skin and internal cancers. In addition to its oncogenic effects, other conditions such as diabetes, peripheral neuropathy, and cardiovascular disease have also been linked to arsenic exposure (Abernathy et al., 1999).
In developed, countries a variety of technologies are currently in use for removal of As from water sources. These technologies include ion exchange, reverse osmosis, adsorption, and electro-dialysis reversal. Though these methods are effective for As removal their complexity and cost precludes their implementation in rural areas and developing countries. Alternative methods used for arsenic removal in developing countries rely primarily of coagulation/filtration. For example, ferric chloride coagulation and filtration is currently in use in some Bangladeshi villages (Adeel and Ali, 2002). Other techniques include batch-mixed treatment with zero-valence iron to reduce arsenic from water (Anuradha et al., 2001). Granular ferric hydroxide has also been tested for the removal of arsenic from drinking water (Driehaus et al., 1998; Thirunavukkarasu et al., 2003). Studies have also been performed to test removal of arsenic from ground water by iron hydroxide-coated sand (Joshi and Chaudhuri, 1996). However, these methods are inadequate to reduce arsenic contamination levels to meet safety levels recommended by the U.S. Environmental Protection Agency (USEPA) (Adeel and Ali, 2002). The dire health effects of arsenic and the implementation of more stringent controls on arsenic levels in drinking water have created a need for an efficient and cost effective means for removal of arsenic from water supplies.